Topic
Wave height
About: Wave height is a research topic. Over the lifetime, 5920 publications have been published within this topic receiving 100257 citations.
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TL;DR: In this paper, a large hump in the pressure spectra is observed at the wave frequencies and the amplitude of this hump increases and the rate of its vertical decay decreases as the mean wind speed increases.
Abstract: Measurements of static pressure and wave height are used to describe the waveinduced pressure field above generating sea waves. A large hump in the pressure spectra is observed at the wave frequencies. The amplitude of this hump increases and the rate of its vertical decay decreases as the mean wind speed increases. The phase difference between the pressure and the waves during active generation is about 135°, pressure lagging the waves, and does not change vertically for measurements at heights greater than the wave crests. In the present data, active wave generation appears to occur only when the wind at a height of 5 metres is greater than or about equal to twice the phase speed of the waves.
75 citations
TL;DR: The goal of this paper is to provide a comprehensive review of the state of the art algorithms for ocean wind and wave information extraction from X-band marine radar data.
Abstract: Ocean wind and wave parameters can be measured by in-situ sensors such as anemometers and buoys. Since the 1980s, X-band marine radar has evolved as one of the remote sensing instruments for such purposes since its sea surface images contain considerable wind and wave information. The maturity and accuracy of X-band marine radar wind and wave measurements have already enabled relevant commercial products to be used in real-world applications. The goal of this paper is to provide a comprehensive review of the state of the art algorithms for ocean wind and wave information extraction from X-band marine radar data. Wind measurements are mainly based on the dependence of radar image intensities on wind direction and speed. Wave parameters can be obtained from radar-derived wave spectra or radar image textures for non-coherent radar and from surface radial velocity for coherent radar. In this review, the principles of the methodologies are described, the performances are compared, and the pros and cons are discussed. Specifically, recent developments for wind and wave measurements are highlighted. These include the mitigation of rain effects on wind measurements and wave height estimation without external calibrations. Finally, remaining challenges and future trends are discussed.
75 citations
TL;DR: In this article, the authors provide coastal engineers and scientists with a quantitative evaluation of nearshore numerical wave models in reef environments, and compare three common- ly used models with detailed laboratory observations.
Abstract: To provide coastal engineers and scientists with a quantitative evaluation of nearshore numerical wave models in reef environments, we review and compare three common- ly used models with detailed laboratory observations. These models are the following: (1) SWASH (Simulating WAves till SHore) (Zijlema et al. 2011), a phase-resolving nonlinear shallow-water wave model with added nonhydrostatic terms; (2) SWAN (Simulating WAve Nearshore) (Booij et al. 1999), a phase-averaged spectral wave model; and (3) XBeach (Roelvink et al. 2009), a coupled phase-averaged spectral wave model (applied to modeling sea-swell waves) and a nonlinear shallow-water model (applied to modeling infragravity waves). A quantitative assessment was made of each model's ability to predict sea-swell (SS) wave height, infragravity (IG) wave height, wave spectra, and wave setup (η) at fivelocationsacross the laboratory fringingreefprofile of Demirbilek et al. (2007). Simulations were performed with the "recommended"empirical coefficients as documented for each model, and then the key wave-breaking parameter for each model (α in SWASH and γ in both SWAN and XBeach) was optimized to most accurately reproduce the observations. SWASH, SWAN, and XBeach were found to be capable of predicting SS wave height variations across the steep fringing reef profile with reasonable accuracy using the default coeffi- cients. Nevertheless, tuning of the key wave-breaking parameter improved the accuracy of each model's predictions. SWASH and XBeach were also able to predict IG wave height and spectral transformation. Although SWAN was capable of modeling the SS wave height, in its current form, it was not capable of modeling the spectral transformation into lower frequencies, as evident in the underprediction of the low- frequency waves.
74 citations
TL;DR: In this paper, a decomposition of the wave spectra into wind sea and swell reveals an average 10% overprediction of the wind sea by the WAM while swell is underpredicted by 20-30%.
Abstract: Ocean wave spectra were retrieved from a set of ERS-I synthetic aperture radar (SAR) wave mode (SWM) spectra between January 1993 and December 1995. An assessment is given of the SWM data quality and the retrieval performance as well as the operational feasibility of the retrieval algorithm. Sensitivity studies are performed to demonstrate the weak residual dependence of the retrieval on the first-guess input spectrum. The mean spectral parameters of the SWM retrievals are compared with spectral parameters from collocated wave model (WAM) spectra. The time series of SWM-retrieved and WAM-derived monthly mean significant wave heights Hs in various ocean basins show good overall agreement but with a small systematic underestimation of Hs by the WAM. A decomposition of the wave spectra into wind sea and swell reveals an average 10% overprediction of the wind sea by the WAM while swell is underpredicted by 20–30%. The positive wind-sea bias exhibits no clear wave height dependence, while the negative swell bias decreases with swell wave height. This could be due to a too strong damping in the WAM at low frequencies. Detailed regional investigations point to the existence of smaller-scale phenomena, which may not be adequately reproduced by the WAM at the present resolution of the wind forcing. Finally, an intercomparison is made of the observed and modeled azimuthal cutoff length scales, and global distributions are investigated. Ratios of the observed azimuthal cutoff wavenumber to the mean azimuthal wavenumber component indicate that about 75% of the swell can be directly resolved by the SAR, while about 70% of the wind sea lies at least partially beyond the cutoff.
74 citations
TL;DR: In this article, the effects of moveable-bed bottom friction for wave observations and wave modeling are investigated using a state-of-the-art bottom friction model, which combines the hydrodynamic friction model of Madsen et al. with a moveablebed roughness model based on Grant and Madsen.
Abstract: Effects of moveable-bed bottom friction for wave observations and wave modeling are investigated using a state-of-the-art bottom friction model. This model combines the hydrodynamic friction model of Madsen et al. with a moveable-bed roughness model based on Grant and Madsen. Analyzing the present model for idealized swell cases, it is shown that swell might result in wave-generated sand ripples. The large change of roughness corresponding to initial ripple formation results in a preferred wave height for swell, related to bathymetric scales as generally occur in shelf seas away from the coast. The corresponding wave-generated bottom roughness is not defined by the local wave conditions, but is related to the overall energy balance of the wave field. Sediment data thus is imperative for the interpretation of observed decay rates and friction factors for swell. For idealized depth-limited wind seas, near-bottom wave motion is expected to generate partially washed-out ripples and moderate sheet-flo...
74 citations